1. Field
The present invention relates to a scaffolding, and more particularly, to a scaffolding for use in building a structure, such as a tank.
2. Discussion of the Related Technology
In general, liquefied natural gas (“LNG”) is obtained by causing natural gas, one of fossil fuels, to be liquefied. An LNG storage tank is classified into a ground storage tank which is installed on the ground or buried in the ground, a mobile storage tank which is installed on a transportation means such as automobiles and ships, and the like, according to installation positions.
The aforementioned LNG is stored in a cryogenic state and is explosive when it is exposed to the impact. Thus, the LNG storage tank should be constructed such that the impact resistance and liquid-tight characteristics thereof can be firmly maintained. The LNG storage tank installed on a moving automobile or ship is slightly different from the ground storage tank with little motion in view of their configurations in that it should take precautions against mechanical stress due to the motion thereof. However, the LNG storage tank, which is installed on a ship and takes precautions against the mechanical stress, can also be used as a ground storage tank. Therefore, the structure of an LNG storage tank installed on a ship will be described herein by way of example.
First, an LNG storage tank installed within an LNG carrier may be classified into an independent tank type and a membrane type. This corresponds to classification according to whether cargo load is applied directly to an insulating material, and detailed descriptions thereof will be hereinafter discussed.
As shown in Table 1, a GT type made in Gaz Transport and a TGZ type made in Technigaz are renamed and used as GTT NO 96-2 and GTT Mark III, respectively, as Gaz Transport (GT) and Technigaz (TGZ) are merged into and renamed as Gaztransport & Technigaz (GTT) in 1995.
TABLE 1Classification of LNG Storage TanksMembrane TypeIndependent TypeItemGTT Mark IIIGTT NO 96-2MOSSIHI - SPBTank MaterialSUS 304LInvar SteelAl Alloy SteelAl Alloy Steelthickness1.2 mm0.7 mm50 mmMax. 30 mmInsulatingReinforcedPlywood Box +PolyurethanePolyurethaneMaterialPolyurethane FoamPerliteFoamFoamthickness250 mm530 mm250 mm200 mm
The structures of the aforementioned GT type and TGZ type tanks are described in U.S. Pat. No. 6,035,795, U.S. Pat. No. 6,378,722, U.S. Pat. No. 5,586,513, U.S. Patent Laid-Open Publication No. 2003-0000949, Korean Patent Laid-Open Publication No. 2000-0011346, and the like. A recent technology for the corner part (edge part) of the LNG storage tank includes “a water-tight and thermally insulating tank with an improved corner structure, built into the bearing structure of a ship” described in Korean Patent Laid-Open Publication No. 2000-0011347. Accordingly, an insulation system installed within a large structure such as an LNG tank of a ship and an insulation system construction method can be explained with reference to the aforementioned patent or patent application.
As described above, a scaffold is set up in order to construct an insulation system within a large structure such as a tank. Here, a scaffold is set up before a large structure is completed, and then provides a sufficient space for workers to have easy access to and to easily perform desired work on the large structure. Such a scaffold is classified into an external scaffold installed outside of a large structure and an internal scaffold installed for the internal construction of a large structure such as a pressure vessel, a tank and a dome. The internal and external scaffolds are slightly different from each other in view of kinds of work, installation structures and the like. FIG. 1 is a schematic view illustrating a state where an exemplary scaffold is installed within a structure. The exemplary scaffold may be the one disclosed in Korean Patent No. 174764.
The discussion in this section is to provide a general background information, and does not constitute an admission of a prior art.